I purchased a gallon of EF-HI a couple of months ago. I diluted it 50% and it is still plenty strong for everything I've tried it on so far. it works great on wheels, even on nasty brake dust coated BMW wheels. I also tried it on the engine of my subaru with great results. the best part is that it's $20/gallon and works great when diluted 50%, bringing the cost down to $10 gallon. :up